The Asian Summer Monsoon: Teleconnections and Forcing Mechanisms—A Review from Chinese Speleothem δ18O Records

Abstract

Asian summer monsoon (ASM) variability significantly affects hydro-climate, and thus socio-economics, in the East Asian region, where nearly one-third of the global population resides. Over the last two decades, speleothem δ 18 O records from China have been utilized to reconstruct ASM variability and its underlying forcing mechanisms on orbital to seasonal timescales. Here, we use the Speleothem Isotopes Synthesis and Analysis database (SISAL_v1) to present an overview of hydro-climate variability related to the ASM during three periods: the late Pleistocene, the Holocene, and the last two millennia. We highlight the possible global teleconnections and forcing mechanisms of the ASM on different timescales. The longest composite stalagmite δ 18 O record over the past 640 kyr BP from the region demonstrates that ASM variability on orbital timescales is dominated by the 23 kyr precessional cycles, which are in phase with Northern Hemisphere summer insolation (NHSI). During the last glacial, millennial changes in the intensity of the ASM appear to be controlled by North Atlantic climate and oceanic feedbacks. During the Holocene, changes in ASM intensity were primarily controlled by NHSI. However, the spatio-temporal distribution of monsoon rain belts may vary with changes in ASM intensity on decadal to millennial timescales.

Deciphering Oxygen Isotope Records From Chinese Speleothems With an Isotope‐Enabled Climate Model

“…We mainly discussed the interpretation of Asian speleothem 18 O at orbital and interannual time scales but did not cover the time scales in between. Asian speleothem 18 O are coherent at millennial scales and follow the Northern Hemisphere insolation variations (Cheng et al, 2012Zhang et al, 2019), so we believe its explanations will be similar with that at orbital scales, which is the migration of the monsoon circulation system. However, the change of regional precipitation patterns may not be the same as the orbital variations.…”

“…Since the pioneering Hulu cave study of Wang et al (2001), which for the first time revealed a well-dated speleothem record in the monsoon region and showed its coherent variability with Greenland ice-cores records, Chinese speleothems have been in the spotlight of the paleoclimate community (Cheng et al, 2009(Cheng et al, , 2012Cosford et al, 2008;Dykoski et al, 2005;Hu et al, 2008;Yuan et al, 2004;. Several Chinese speleothem 18 O records are continuous, dating back to 600 kyr ago, coinciding well with Northern Hemisphere summer insolation intensity and dominated by precessional cycles (23 kyr) (Cheng et al, 2009(Cheng et al, , 2012Zhang et al, 2019). The interpretation of these records remains in intense debates Liu et al, 2014).…”

“…Despite this complexity, many studies have noted that speleothem 18 O at orbital scales is coherent across Asia, closely tracking Northern Hemisphere summer insolation (Battisti et al, 2014;Cheng et al, 2012Cheng et al, , 2016. However, this coherency vanishes at scales shorter than millennial (Chu et al, 2012;Li et al, 2014;Wan et al, 2011;Zhang et al, 2019). This raises the question of what governs Asian speleothem understanding and improved projections of hydroclimate variability in Asia, which affects the water supply of over 4 billion people.…”

A Brief Commentary on the Interpretation of Chinese Speleothem δ18O Records as Summer Monsoon Intensity Tracers

“…The interpretation that negative excursions in the cave δ 18 O records reflect changes in the amount of monsoon rainfall alone is only partially supported [11,12] and remains widely contested [13]. The Zhang et al study also does not address evidence from recently published marine and terrestrial proxy records of monsoon precipitation from the EASM and ISM domains [14,15], which are at odds with the major conclusions drawn therein [1].Early reconstructions of Asian summer monsoon intensity were based on proxies of wind strength over the Arabian Sea [16][17][18]. These results were interpreted to infer changes in the intensity of monsoon precipitation over land given that strong summer monsoon winds promote upwelling-driven productivity in the Arabian Sea [19], and transport large amounts of moisture to the Asian continent [20].…”

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Zhang et al [1] argue that changes in northern hemisphere summer insolation (NHSI) caused by the precession of Earth's orbit have controlled the timing and pace of the late Pleistocene East Asian summer monsoon (EASM) and Indian summer monsoon (ISM). Since the early 2000s, several high-resolution cave δ 18 O records from China dated with unprecedented precision have been published [2][3][4][5] and are widely interpreted as proxies for East Asian summer monsoon (EASM) intensity [5].

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